This is a comprehensive review on the pigs’ normal eliminatory behaviour (i.e., defaecation and urination) and pen soiling. This review is aimed primarily at solving issues with pen soiling in current systems, and ultimately at the future design of a well-functioning pig toilet, which we intend to elaborate on in a subsequent publication. In this paper, first, normal elimination is described in relation to what is known about its phylogeny, ontogeny, causation, and function, i.e., according to Tinbergen’s four why questions concerning animal behaviour. Then, pen soiling is described as if it were a medical disorder, highlighting its importance, aetiology, symptoms, diagnosis, pathogenesis, treatment, and prevention. Due to its negative consequences in terms of animal welfare, health, workload, and environmental emissions, possible methods to address pen soiling in current systems are described. Probably, pigs do not choose a specific place to eliminate but rather choose the most comfortable place for resting, and avoid eliminating there. We identified four main strategies to reduce pen soiling: (1) reducing the suitability of the designated elimination area to be used for other functions, especially resting or thermoregulation; (2) improving the suitability of other functional areas in the pen to be used for their specific function, such as resting and activity; (3) reducing the suitability of other functional areas to be used for elimination; and (4) improving the suitability of the elimination area for elimination. These prevention strategies and the encompassing disease framework provide a structured approach to deal with pen soiling in existing systems and to support the future design, development, and implementation of a well-functioning pig toilet that can help to achieve some of the main goals of modern pig production, namely reducing environmental emissions as well as substantially improving pig welfare.

Confinement to farrowing crates is known to prevent sows from performing natural behavior, impairing animal welfare and possibly causing chronic stress. Hair cortisol analyses are increasingly used to detect chronic stress in animals. In the present study, hair samples were collected in the neck of sows kept either in farrowing crates (FC,n= 31) or in a loose-housing system (LH,n= 30) in six batches. Cortisol was extracted and analyzed using chemiluminescence immunoassay. Mean hair cortisol concentrations (HCC) did not differ significantly between the systems (LH: 1.85 ± 0.82 pg/mg, FC: 2.13 ± 1.53 pg/mg,P= 0.631). HCC was also not affected by other factors, such as sows' parity, number of piglets, skin lesion score or sow's weight loss during the farrowing period. However, highly significant differences were found in hair growth rates between different regions within the 20 × 30 cm shaving area. While the hair in both lateral parts of the shaving area grew almost identically (left: 7.48 ± 3.52 mm, right: 7.44 ± 3.24 mm,P= 1.00), the hair grew more in the area above the spine (12.27 + 3.95 mm,P< 0.001). In both systems, the mean individual lesion score of sows declined from the beginning to the end of the housing period (P< 0.001). No difference was found between FC and LH sows at any time (P> 0.05). Since neither the amount of skin lesions nor HCC differed between LH and FC sows, it may be concluded that confining sows in farrowing crates did not affect chronic stress levels. However, results may be affected by a downregulation of the hypothalamic-pituitary-adrenal axis during long-term stress, resulting in lower cortisol levels over time. HCC in sows may also be influenced by a dominant stressor, such as farrowing or the presence of suckling piglets. Thus, for a comparison of different farrowing systems regarding chronic stress, the use of hair cortisol measurement seems to be limited. The present results revealed that differences in hair growth rate within the same body region exist. This important finding should be considered when collecting hair samples in pigs, since hair cortisol concentrations may vary depending on hair growth and length.

Pens with farrowing crate (FC) and two differently designed free-farrowing pens (LH-pens: 7.3 m², plastic flooring; GH-pens: 5 m², cast-iron and concrete flooring) were compared regarding piglet losses and postpartum sow behaviour (all treatments) and reasons for piglet crushing and postpartum litter behaviour (LH and GH). One-hundred-and-three crushing events were analysed in eight batches concerning sows’ posture changes that crushed piglets and age of crushed piglets. Posture change frequency, amounts of single posture changes and total time spent in different body postures were evaluated for 41 sows (14 FC-sows, 13 LH-sows and 14 GH-sows) in six batches. Litter behaviour (location, active/inactive scoring, resting behaviour next to the sow) was analysed during sows’ posture changes and piglet crushing. Piglet mortality was higher in LH (25.6%) and GH (19.9%) compared to FC (12.3%) due to higher levels of piglet crushing. Most crushing occurred during the three days postpartum in LH (92.7%) and GH (83.9%). However, crushing patterns differed between LH (rolling: 68.2%; sit-to-lie: 18.2%; stand-to-lie: 11.4%) and GH (rolling: 38.2%; sit-to-lie: 30.9%; stand-to-lie: 16.4%) and varying piglet behaviour may be the cause for this. The postpartum period was characterized by inactivity of the sow and behavioural differences were rarely seen between systems.

The aim of the present study was to develop and evaluate a new housing system for fattening rabbits. Data were collected on a farm with rabbits housed either under new conditions (NC) or established (conventional) conditions (CC). NC housing was characterized by large groups (Ø 58 rabbits, max. 12 rabbits/m²), slatted plastic floor (11 mm slats and 11 mm gaps), elevated platforms with partly solid floor, boxes and different enrichment materials. CC rabbits were kept in small groups (eight rabbits, 23 rabbits/m²) in cages with wire-mesh floor, an elevated platform, a box and one gnawing stick. Skin lesions and weight gain of 524 rabbits, cleanliness of their hind feet as well as their mortality and morbidity were investigated from weaning to slaughter in five batches. The evaluations showed higher daily weight gain (46.3 ± 6.0 g vs. 43.1 ± 5.5 g) and final weight (2878 ± 328 g vs. 2707 ± 299 g), as well as a lower cumulative lesion score at the middle of the fattening period in NC than in CC rabbits. Nevertheless, cleanliness of hind feet was assessed to be worse and mortality was higher in the NC housing. The NC system provided some benefits in terms of animal welfare compared to the conventional system, but hygienic challenges posed by this system make further adjustment necessary.

The aim of this study was to analyse a novel group farrowing system (GH) concerning piglets’ behaviour, skin injuries and body weight gain, to test its animal friendliness. Skin injuries and weight gain were compared to piglets originating from conventional individual housing (IH) before and after weaning. The GH system had five farrowing pens without crates, a common area and an area only available for piglets. In total, 34 litters were studied. Four days after the GH-piglets had left the pens during lactation, the lesion score of piglets in GH was higher than in IH. However, piglets from the GH sustained fewer injuries after mixing at weaning, compared to the piglets from IH and had higher daily weight gains, during the early nursery phase. The common area in GH was intensively used for active behaviour, since standing/walking and playing were observed there, most frequently, whereas lying occurred most frequently inside the pens. Immediately after the piglets had left the pens in the GH, the piglets preferred proximity to the sow, compared to the pens where they were born. The GH system enabled social enrichment, offered increased space for activity and led to fewer skin lesions, after weaning; thus, potentially increasing animal welfare.

It is known that pigs raised in enriched environments express less aggressive behaviour. For this reason, a new method of cognitive environmental enrichment was experimented at the University of Veterinary Medicine Hannover, Germany. In the first phase, 78 suckling piglets were trained to learn the link between a sound given by an electronic feeder and a feed reward in the form of chocolate candies during a period of 8 days. In the second phase, the same piglets were used in resident-intruder tests to verify the potential of the feeding system to interrupt aggressive behaviour. The analysis of all training rounds revealed that piglets learned the commands during 8 days of training and the interest of the piglets increased within training days (P<0.05). In the resident-intruder test, 79.5% of aggressive interactions were broken by feeder activation. In interactions where either the aggressor or the receiver reacted, a high number of fights were stopped (96.7% versus 93.1%) indicating that it was not relevant if the aggressor or the receiver responded to the feeder activation. We conclude that the electronic feeding system has the potential to be used as cognitive enrichment for piglets, being suitable for reducing aggressive behaviour in resident-intruder situations.